I have a MBP (15" Mid 2010) running 10.8 attached to a 27" Samsung external monitor via HDMI connection (through an adapter cord).
I have my display timeout set to 3 minutes (shorter than my sleep, which is 15 minutes). When the 3 minute mark is hit, the laptop screen goes black as expected but the external monitor "freezes" on the frame it was currently displaying. I can tell it's frozen and not just on because the clock doesn't move and any other animations are suspended. When I move the mouse to "wake" the laptop, the screen resumes without anu noticeable delay.
Has anyone else had this? Any known or suggested fixes?